In 1976, Professor Kaminsky of Germany reported that olefin polymerization could be accomplished using a zirconocene dichloride compound as a catalyst with methylaluminoxane (MAO), which was obtained through partial hydrolysis of trimethylaluminum, as a co-catalyst. See A. Anderson, et al., Angew. Chem., Int. Ed. Engl. 15, 630 (1976). Thereafter, Exxon showed that the activity of a catalyst and the molecular weight of the resulting polymer could be controlled by changing the substituents on the cyclopentadienyl ligand, and secured a patent (U.S. Pat. No. 5,324,800) on olefin polymerization utilizing the specified metallocene compounds with various substituent groups.
A homogeneous metallocene catalyst exhibits unique polymerization characteristics which cannot be obtained by conventional Ziegler-Natta catalysts. That is, the molecular weight distribution of the resulting polymer is narrow, co-polymerization is easy, and the co-monomer distribution is uniform. In the case of propylene polymerization, the tacticity of polymer can be controlled via the molecular symmetry of catalyst. These unique characteristics not only opened up a way to produce new polymers which are not attainable by conventional Ziegler-Natta catalysts, but also provided a way to make tailor-made polymers. Accordingly, there has been continuous interest in this catalyst system.
In a gas phase or a slurry process, particle morphology and the bulk density of the polymer are preferably controlled to increase the mobility of polymer and the production rate per reactor unit volume. Also, reactor fouling, a phenomenon wherein polymer sticks to the reactor wall and agitator blades, is preferably avoided for a continuous operation. To solve these problems, the catalyst is preferably anchored on a suitable support.
The following are conventional preparation methods for supported metallocene catalysts: 1) a metallocene compound is adsorbed on a support, and then activated by treatment with aluminoxane (W. Kaminsky, Makromol. Chem., Rapid Commun. 14, 239 (1993); 2) aluminoxane is supported first, and then a metallocene compound is supported (K. Soga, Makromol. Chem. Rapid Commun. 13, 221 (1992); U.S. Pat. No. 5,006,500; U.S. Pat. No. 5,086,025); 3) a metallocene compound is treated with aluminoxane, and then adsorbed on a support (U.S. Pat. No. 5,240,894); and 4) the anchoring of catalyst is achieved by a chemical reaction between the ligand of a metallocene compound and a support.
In one method, the metal is ligated after the ligand is supported. (K. Soga, H. J. Kim, T. Shiono, Makromol., Rapid Commun. 15, 139 (1994), Japanese Laid-open Patent No. Heisei 6-56928, U.S. Pat. No. 5,466,766). In the other methods, a metallocene compound with suitable ligands is prepared and then it is supported on a support by chemical reaction. The suitable ligands in this case usually contain silicon based functional groups such as alkoxysilane or halosilane (European Patent No. 293815, U.S. Pat. No. 5,202,398, U.S. Pat. No. 5,767,300, European Patent No. 839836, Korean Patent Application Nos. 98-12660 and 99-06955). However, metallocene compounds with silicon containing functional group are not easy to make and do not have good stabilities. For example, European Patent No. 839836 discloses a metallocene compound having the functional group —OSiMe3. The yield in the metallation step, which is the last step in the synthesis, is only around 28 to 51% which is a disadvantage in commercial applications.
U.S. Pat. No. 5,814,574 discloses a supported polymerization catalyst which is prepared by the binding of an inorganic support with a metallocene compound containing a functional group selected from alkoxyalkyl, heterocycle oxygen group, and alkyl heterocycle oxygen group. U.S. Pat. No. 5,767,209 discloses the polymerization of olefins at a specified temperature and pressure utilizing a supported catalyst. In this patent, the metallocene compound with Lewis base functionalities, such as oxygen, silicon, phosphorus, nitrogen or sulfur atoms, is bound to an inorganic support in the absence of aluminoxane to give a supported catalyst. However, the catalyst bound to and supported on the inorganic support surface by the Lewis acid-base reaction leaches out of the surface upon activation with a Lewis acidic aluminoxane co-catalyst. The leaching of the catalyst results in reactor fouling and irregular morphology, which are detrimental in a slurry or a gas phase process.
Metallocene catalysts with suitable functional groups can be supported on a silica surface by the reaction of an alkoxysilane or halosilane functional group with a surface hydroxyl group or highly reactive siloxane group, which is formed from the dehydroxylation of the silica above 600° C., as shown in Reaction Formulas 1 through 3.



EP 293815 A1 discloses a method in which a supported metallocene catalyst is prepared by the reaction of a metallocene compound containing a —C—SiR2(OR′) functional group (wherein R is a C1-4 alkyl, C6-10 aryl, or C1-4 alkoxy, and OR′ is a C1-4 alkoxy) with a support hydroxyl group on its surface, as depicted in Reaction Formula 4.

In this reaction, a Si—OR′ (silicon-based group) bond of the metallocene compound is reacted with a Si—OH group of the support material to produce a strongly bound, supported metallocene catalyst via Si—O—Si bond formation. However, an alkyl alcohol (R′OH) by-product is also formed during the reaction, and can act as a catalyst poison to lower activity of the resulting catalyst.
Reaction Formula 3 has been reported recently (J. Am. Chem. Soc. 117, 2112, (1995); J. Am. Chem. Soc. 115, 1190, (1993)) and is advantageous in the preparation of a supported metallocene catalyst because side reactions are minimized (Korean Patent Application No. 98-12660). As mentioned above, however, the catalyst with siloxane functional groups is not easy to make and has low stability. For example, catalysts containing an alkoxysilane group, [HMe2Si—O—(CH2)6—C5H4]2ZrCl2 and [Me3Si—O—(CH2)6—C5H4]2ZrCl2, were disclosed in the examples and comparative examples of Korean Patent Application No 99-06955. In the examples, the yield in the zirconation step, which is the last step of the synthesis, was below 60% and the catalysts were observed to degrade slowly over an extended period of time under an inert gas atmosphere at room temperature. Other catalysts are disclosed in J. Organomet. Chem. 552, 313, (1998).